The present invention relates generally to a feedblock for an extrusion die, and more particularly to a feedblock for creating a multi-layer polymeric sheet wherein the dimensions of at least some of the layers are adjustable.
Extrusion processes generally involve forcing a viscous material through a die typically comprising an inlet, a cavity, and an exit. In many instances, the end-product of the extrusion process is a sheet comprising a single layer of polymeric material. In other instances, however, it is desirable to produce a sheet of formable material having a plurality of distinct layers that comprise different materials having different properties. By using different materials having different properties to create each layer, the resulting multi-layer sheet has the combined properties of all of the layers. For example, it may desirable to create a food wrap bars oxygen so that food stored therein remains fresh. However, materials that act as oxygen barriers are typically structurally weak. Thus, it may be desirable to create a food wrap that acts as an oxygen barrier and that is structurally strong by combining a layer made from a material having the. characteristics of an oxygen barrier with a layer made from a material that is known for its structural integrity and strength.
Methods known in the art for creating multi-layer sheets typically involve combining a plurality of polymeric streams wherein each stream comprises a different material and wherein each stream forms a distinct layer of the sheet. More advanced methods for creating multi-layer sheets additionally include ways to control and adjust the dimensions of the co-extruded layers of a multi-layer sheet. Controlling and adjusting the dimensions of the co-extruded layers is useful for a variety of reasons including, for example, to further affect the properties of the resulting multi-layer sheet. More specifically, depending upon the materials used to form the layers, the thickness of the layers may affect the surface finish of the resulting multi-layer sheet causing it to be either clear or opaque. In addition, it is necessary to ensure that the dimensions of the various layers are consistent throughout the sheet to ensure that the properties of the resulting multi-layer sheet are uniform throughout the sheet. Also, it is necessary that the layer widths be equal and precisely positioned so that uniformity is maintained at the edges of the sheet. In addition, dimension control can also be used to control fabrication costs. As an example, a base material may be coated with a layer of resin that shields the base material from UV rays. The protective resin layer must be at least of a minimum thickness in order to achieve adequate UV protection. However, UV protective resins are costly, and therefore it is desirable to use only as much as needed to obtain the required level of UV protection. Accordingly, precise dimensional control over layer thickness is required so that costs are minimized.
Murakami U.S. Pat. No. 4,669,965 discloses a multi-layer extrusion die having an integrate that resides within a cavity of the die body and that comprises a set of flat plates disposed on top of one another. To produce a multi-layer sheet, a stream of resin is supplied to a flow inlet disposed in each plate and the stream thereafter flows into a downstream portion of the plate having a wide and flat geometry. As the resin stream enters the downstream portion of the plate it conforms to the wide and flat geometry of the downstream portion thereby causing individual layer-like streams to form in each plate. The layer-like streams then enter into a flow-combining zone where the streams are deposited one on top of the other. The dimensions of the layers, such as the width or thickness of the various layers, are dictated by the geometry of the plates and the flow passages of the die. To create a set of layers having a desired width or thickness, a set of suitably sized plates must be fabricated and inserted into the integrate which is then inserted into the die body. However, to create a new set of layers having a different set of dimensions, a different, properly sized set of plates must be fabricated for insertion into the integrate.
Similarly, Blemberg U.S. Pat. No. 5,236,642 discloses an apparatus comprising an encapsulator, a feedblock and a die wherein two melt streams are combined in the encapsulator to produce an encapsulated layer element that is thereafter supplied to the feedblock 62 via an elongate transport pipe. Within the feedblock 62, the encapsulated layer element is combined with yet another stream and the resulting layered stream thereafter flows into a main channel disposed within the die body. The main channel converges with two auxiliary flow channels that are also disposed within the die body such that the materials flowing in the two auxiliary flow channels combine with the layered stream of the main channel to form a multi-layer sheet. Like Murakami, Blemberg et al. also teaches that the dimensions of the individual layers are a function of the geometry of the flow passages within the feedblock or die. More particularly, Blemberg et al. reduces the variations in the thickness of a layer by passing the layered stream that exits the encapsulator through the elongate transport pipe. According to Blemberg et al., passing the stream through the elongate transport pipe tends to automatically correct any asymmetry, non-concentricity or other non-uniformity which may exist in the combined melt stream as it leaves the encapsulator, thereby resulting in a more uniform melt stream thickness. In addition, Blemberg et al. teaches that the thickness of a set of two layers can be adjusted by altering the flow rates of the two streams that form the individual layers.
However, methods that rely upon the geometry of fixed flow channels in a feedblock or die to produce a sheet with layers having a desired set of dimensions are of limited value because the dimensions of the streams, and thus, the layers, cannot be adjusted without changing the geometry of the flow channels. This, in turn, requires the design and fabrication of a different feedblock or die. In addition, methods that rely upon the relative flow rates of the streams to adjust the dimensions of the layers require that new flow rates be established for each stream in order to achieve the new set of desired dimensions.
Other advantages of the invention will be apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings and the appended claims.
In accordance with one aspect of the present invention, a feedblock includes a first passage defining a first flow path and a second passage defining a second flow path in fluid communication with the first flow path. In addition, a rotatable member having a passage therethrough forms at least a part of the second flow path and terminates at a convergence zone at which the second flow path meets the first flow path. Rotation of the rotatable member changes a size of the convergence zone.
Preferably, the rotatable member comprises a hollow spool. Also preferably, the convergence zone is defined by an opening in the rotatable member. Further, the opening in the rotatable member may be contoured or rectangular.
Still further in accordance with the preferred embodiment, the feedblock includes an adjustment apparatus coupled to the rotatable member. Also, the adjustment apparatus may include an adjustment lever coupled to the rotatable member and an adjustment screw threaded into a bore carried by the adjustment lever. In addition, the adjustment apparatus may further include indicating apparatus coupled to the rotatable member and operable to indicate a position of the rotatable member.
Also, according to the preferred embodiment, the feedblock may additionally include an adapter coupled to the second flow path by which a formable material is supplied to the second flow path.
Preferably, the feedblock further includes a third flow passage defining a third flow path that is also in fluid communication with the first flow path and a second rotatable member having a passage therethrough. The passage of the second rotatable member forms at least a part of the third flow path and terminates at a second convergence zone at which the third flow path meets the first flow path. Rotation of the second rotatable member changes a size of the second convergence zone.
In addition, to the foregoing, the feedblock may further include a set of heaters disposed within a body of the feedblock and disposed parallel to a portion of the first flow path that is located downstream of the convergence zone. The set of heaters may be controllable to control a viscosity of a formable material flowing through the portion of the first flow path that is located downstream of the convergence zone.
In a further embodiment of the present invention, a feedblock may include a primary passage defining a primary flow path, and a plurality of secondary passages, each defining one of a plurality of secondary flow paths that are in fluid communication with the primary flow path. The feedblock may further include a plurality of rotatable members, each rotatable member having a channel therethrough that forms at least a part of one of the secondary flow paths and each of the channels terminating at one of a plurality of convergence zones, wherein each convergence zone is defined by a region in which one of the secondary flow paths meets the primary flow path and wherein rotation of each of the rotatable members changes a size of a corresponding one of the convergence zones.